Dash insulators are often mounted in motor vehicles inside the passenger compartment and against a metallic fire wall which separates the passenger compartment from an engine compartment. The primary purpose of the dash insulator is to reduce the transmission of noise and heat from the engine compartment into the passenger compartment. To address this purpose, conventional dash insulators consist of an acoustical absorber such as an open-cell polyurethane foam or a resinated fiber pad which faces the fire wall, and a barrier such as a heavily filled thermoplastic material. Mechanical fasteners, stiffeners and spacers may also be attached to the dash insulator.
Dash insulator barriers are conventionally produced in a compounding process followed by an extrusion or calendering process to achieve a barrier sheet of desired thickness and width. The sheet is bonded to a foam slab stock using an appropriate adhesive. It is then heated under infrared heaters, thermoformed in a three-dimensional mold, trimmed on a trim press and then provided with the necessary attachments in an assembly process. Alternatively, the slab foam sheet may be replaced by a foam-in-place polyurethane absorber. In this alternative process, the barrier sheet is first thermoformed, and then a urethane foam is injected behind the thermoformed barrier sheet. That subassembly is then cured, trimmed and finished as in the above case.
In another alternative, a standard injection molding process is used to produce the three-dimensional barrier, and then the urethane foam absorber is glued to the barrier. Because the parts are very large, and the wall thicknesses are very low, it is necessary to use very large tonnage injection molding machines, i.e. on the order of 2000 to 4000 tons.